One method the industry currently uses to manufacture aliphatic amines is the catalytic hydrogenation of aliphatic nitrites, e.g., cyanoethylated amines in either batch or trickle bed hydrogenation equipment. To selectively form primary amines such as dimethylaminopropyl amine (DMAPA) from the precursor nitrile, ammonia is generally used to control the ratio of primary to secondary amine. However, substantial amounts of ammonia are needed to be effective, and even then, several percent of secondary amine coproduct is formed. The handling of ammonia is expensive in that it requires pressurized storage, increases cycle time for loading and venting and it can present an environmental problem unless expensive recovery equipment is provided. Thus, there has been a desire to find ways to effect the hydrogenation of nitrites without the use of ammonia.
Representative patents which illustrate various procedures for the catalytic hydrogenation of nitrites are as follows:
U.S. Pat. No. 4,375,003 discloses a catalytic process for preparing amines by reacting an aliphatic nitrile and hydrogen in the presence of a sponge cobalt catalyst. The improved catalysts employed for the hydrogenation of the aliphatic nitriles are based upon cobalt-aluminum alloys which have been contacted with an alkali metal hydroxide dispersed in an aqueous medium. The examples show the addition of sodium hydroxide solutions to the cobalt-aluminum alloy which catalyst is then used to catalyze the hydrogenation reaction.
U.S. Pat. No. 3,821,305 discloses a process for the catalytic hydrogenation of the adiponitrile to form hexamethylenediamine by carrying out the hydrogenation in the presence of a sponge catalyst and caustic alkali where the hydrogen and the adiponitrile are fed into a liquid reaction medium consisting of hexamethylenediamine, water and the caustic alkali and catalyst. The catalyst employed is a sponge nickel catalyst. The examples show the use of sodium hydroxide as the caustic alkali.
U.S. Pat. No. 3,223,735 discloses a process for the catalytic hydrogenation of a reaction product of acrylonitrile and ammonia to form 1,3-propylene diamine. A wide variety of group Vb, Vlb, Vllb and Vlllb metals are taught as being suited for practicing the hydrogenation process. A large excess of ammonia is used in the process to avoid the formation of secondary amines.
U.S. Pat. No. 5,075,507 discloses a process for the cyanoethylation of glycols to produce bis(cyanoethylated)aliphatic glycols followed by reaction with hydrogen to form bis(aminopropyl)aliphatic glycols. In terms of effecting the reduction of the cyano group of the cyanoethylated glycol, the hydrogenation is carried out using a hydrogenation catalyst such as sponge nickel, palladium, platinum, ruthenium, rhodium and cobalt. Ammonia is charged to the reaction medium to maintain high yield and selectivity.
U.S. Pat. No. 3,427,356 discloses a process for producing 1,3-propylene diamines using cobalt or nickel catalysts. The improvement in their process involves the addition of a small amount of manganese dissolved in the reaction medium.
U.S. Pat. No. 5,254,737 discloses a continuous process for preparing secondary amines from nitriles. The secondary amines are prepared by carrying out the reactions in the presence of ammonia and hydrogen in the first stage and then effecting hydrogenation in the absence of ammonia. The catalyst employed in the reaction is either nickel or cobalt.